Dispensers for delivering a beneficial agent to an environment of use are known to the prior art. For example, one dispenser is disclosed in U.S. Pat. No. 3,995,632 issued to patentees Nakano, Higuchi and Hussain. This patent discloses a dispenser comprising a saturated solution of magnesium sulfate that pushes against a melting composition. The melting composition is squeezed through a small passageway from the dispenser. In U.S. Pat. No. 4,251,506 issued to patentee Laby, a device is disclosed consisting of a controlled release composition for administering a therapeutic agent to a ruminant. The patentee discloses in detail a spring for pushing a composition from the dispenser. The use of a spring as a driving force limits the practical use of the device, as the driving force of a spring diminishes by the distance through which the spring operates. For this device, drug delivery decreases over time as the spring elongates and, concurrently, weakens. The delivery rate is influenced also by the nature of the composition and its interaction with fluid as the interfaced environment of use. The interfaced provides exterior mechanical action that controls drug released by the environment and not by the device.
Another dispenser is disclosed in U.S. Pat. No. 4,327,725 by the inventors Cortese and Theeuwes. The dispenser disclosed in this patent comprises a hydrogel that urges an aqueous formulation through a passageway from the dispenser. In U.S. Pat. No. 4,350,271 issued to Eckenhoff, a dispenser is disclosed comprising a water swellable composition that pushes a lipophilic fluid from the dispenser. U.S. Pat. No. 4,612,008 issued to Wong, Barclay, Deters and Theeuwes discloses a dispenser wherein an expanding polymer pushes a drug formulation comprising an aqueous osmotically active solution from the dispenser. Another dispenser is disclosed by patentees Eckenhoff, Cortese and Landrau in U.S. Pat. No. 4,595,583. The dispenser disclosed in this patent comprises an expandable, aqueous activated osmopolymer that urges a heat responsive composition through an orifice of predetermined limited dimensions from the dispenser.
The release of uncoated pellets of drug and coated pellets of drug is disclosed by patentee Blythe in U.S. Pat. No. 2,738,303. In this patent the delivery system disclosed consists essentially of a capsule containing uncoated pellets and coated pellets of drug having varying thickness. On release of the pellets from the capsule the uncoated pellets provide an initial amount of drug and the coated pellets provide drug over a period of time. Another delivery system is disclosed by patentee Sheth et al in U.S. Pat. Nos. 4,140,775 and 4,167,558. The systems disclosed in these patents consist essentially of a tablet formed of a compressed polymer containing dispersed drug. The system is hydrodynamically balanced for remaining in the stomach for releasing drug over time.
The delivery systems of the prior art presented above represent an outstanding and pioneering advancement in the dispensing art and they are, additionally, useful for dispensing innumerable beneficial agents to an environment of use. Now, this present invention has discovered unexpectedly that a dispenser can be made available comprising a novel and an unobvious dispensing means unknown heretofore for delivering a beneficial agent to an environment of use. That is, it now has been discovered that a dispenser can be provided comprising means for delivering a bio-affecting beneficial agent at a kinetically controlled rate substantially equal to its kinetic rate of release from the dispenser. The dispenser thereby makes available to a beneficial agent receptor controlled and constant prolonged delivery of a beneficial agent according to a preselected built-in optimal program of beneficial agent presentation.